RF electrodes on multiple flexible wires for renal nerve ablation

ABSTRACT

A catheter includes a flexible shaft having a distal end dimensioned for deployment within a patient&#39;s renal artery. A number of elongated resilient members are mounted along a longitudinal length of the distal end of the shaft, and are extensible radially from the shaft at regions defined between longitudinally spaced-apart engagement locations. One or more electrodes are mounted on each of the resilient members at the radially extensible regions. A number of conductors are electrically coupled to the electrodes and extend along the shaft of the catheter. The elongated resilient members are collapsible when encompassed within a lumen of an outer sheath and extensible radially outward from the shaft at the regions defined between the longitudinally spaced-apart engagement locations when the catheter and the resilient members are axially extended beyond the distal tip of the sheath. RF energy is delivered to the electrodes for ablating perivascular renal nerves.

RELATED APPLICATIONS

This application claims the benefit of Provisional Patent ApplicationSer. Nos. 61/369,458 filed Jul. 30, 2010 and 61/418,667 filed Dec. 1,2010, to which priority is claimed pursuant to 35 U.S.C. §119(e) andwhich are hereby incorporated herein by reference in their entirety.

SUMMARY

Embodiments of the disclosure are generally directed to apparatuses andmethods for ablating target tissue of the body from within a vessel.Embodiments are directed to high frequency AC (e.g., radiofrequency(RF)) ablation catheters, systems, and methods that employ electrodes onmultiple flexible wires for enhanced apposition of electrodes within atarget vessel, particularly for irregularities along the inner wall ofthe vessel. Various embodiments of the disclosure are directed toapparatuses and methods for ablating perivascular renal nerves, such asfor treatment of hypertension.

According to various embodiments, an apparatus for delivering ablationtherapy includes a sheath having a lumen and a length of the shaftsufficient to access a target vessel within a patient relative to apercutaneous access location. A catheter comprises a flexible shafthaving a proximal end, a distal end, and a length, the length of theshaft sufficient to access the target vessel relative to thepercutaneous access location. The shaft is dimensioned for displacementwithin the lumen of the sheath and extendible beyond a distal tip of thesheath.

The apparatus includes a plurality of elongated resilient members eachmounted along a longitudinal length of the distal end of the shaft. Theresilient members engage the shaft at a number of longitudinallyspaced-apart locations and are extensible radially from the shaft atregions defined between the longitudinally spaced-apart engagementlocations. One or more electrodes are mounted on each of the resilientmembers at the radially extensible regions. A number of conductors areelectrically coupled to the electrodes and extend along the shaft of thecatheter. The elongated resilient members are collapsible whenencompassed within the lumen of the sheath and extensible radiallyoutward from the shaft at the regions defined between the longitudinallyspaced-apart engagement locations when the catheter and the resilientmembers are axially extended beyond the distal tip of the sheath.

In accordance with some embodiments, an apparatus includes a sheathhaving a lumen and a length sufficient to access a patient's renalartery relative to a percutaneous access location. A catheter comprisesa flexible shaft having a proximal end, a distal end, and a length, thelength of the shaft sufficient to access a patient's renal arteryrelative to the percutaneous access location, The shaft is dimensionedfor displacement within the lumen of the sheath and is extendible beyonda distal tip of the sheath.

The apparatus includes a number of elongated resilient members eachmounted along a longitudinal length of the distal end of the shaft. Theresilient members engage the shaft at a number of longitudinallyspaced-apart locations and are extensible radially from the shaft atregions defined between the longitudinally spaced-apart engagementlocations. One or more electrodes are mounted on each of the resilientmembers at the radially extensible regions. A number of conductors areelectrically coupled to the electrodes and extend along the shaft of thecatheter. The elongated resilient members are collapsible whenencompassed within the lumen of the sheath and extensible radiallyoutward from the shaft at the regions defined between the longitudinallyspaced-apart engagement locations when the catheter and the resilientmembers are axially extended beyond the distal tip of the sheath.

These and other features can be understood in view of the followingdetailed discussion and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a right kidney and renal vasculatureincluding a renal artery branching laterally from the abdominal aorta;

FIGS. 2A and 2B illustrate sympathetic innervation of the renal artery;

FIG. 3A illustrates various tissue layers of the wall of the renalartery;

FIGS. 3B and 3C illustrate a portion of a renal nerve;

FIG. 4A illustrates an apparatus for ablating target tissue of a vesselof the body in accordance with various embodiments;

FIG. 4B illustrates an apparatus for ablating target tissue of a vesselof the body in accordance with various embodiments;

FIG. 4C shows the elongated resilient members of a ablation treatmentelement in a collapsed configuration when encompassed within the lumenof a sheath or a target vessel;

FIGS. 5 and 6 illustrate the distal end of a catheter shaft whichsupports a wire segment arrangement and a retraction mechanism inaccordance with low-profile embodiments of the disclosure;

FIGS. 7 and 8 illustrate a catheter which includes a multiplicity ofelectrodes supported by a wire segment arrangement and having a tissuedisplacing feature in accordance with various embodiments;

FIGS. 9 and 10 illustrate arrangements that facilitate controllableexpansion and retraction of a wire segment arrangement in accordancewith various embodiments;

FIG. 11 illustrates a resilient member having an insulating sleeve orcoating in accordance with various embodiments;

FIGS. 12-15 illustrate various embodiments of an ablation treatmentelement which includes a multiplicity of resilient members mounted in astructurally cooperative configuration relative to one another; and

FIG. 16 shows a representative RF renal therapy apparatus in accordancewith various embodiments.

DISCLOSURE

Embodiments of the disclosure are directed to apparatuses and methodsfor ablating target tissue from within a vessel. Embodiments of thedisclosure are directed to apparatuses and methods for ablating ofperivascular renal nerves from within the renal artery for the treatmentof hypertension. Embodiments of the disclosure include wire segmentstructures that support a multiplicity of electrodes for deliveringrenal nerve ablation.

Obtaining good contact with the artery wall during ablation ofperivascular renal nerves has been difficult. If contact is variable,the tissue temperatures are not well controlled, and an ablativetemperature may not be achieved in the target tissue, while temperaturein other areas, such as portions of the artery wall, may deviate enoughto cause unwanted arterial tissue injury. For ideal anatomy, good vesselapposition can be achieved more easily, but especially with tortuous ordiseased renal arteries, there can be very poor contact to effectivelyand predictably transfer electrical current from an ablation device tothe tissue. Controlled ablation at multiple discrete regions may bedesired to reduce arterial injury, without requiring multiplerepositioning and ablation cycles. There is continued need for improvedvessel wall contact and multi-site ablation for nerve ablation and othertherapies.

Embodiments of the disclosure are directed to apparatuses and methodsfor multi-site RF ablation of perivascular renal nerves for hypertensiontreatment. According to various embodiments, an intravascular catheterdevice has multiple wire segments near the distal end which move betweenlow-profile introduction configuration and larger-diameter deployedconfiguration. One or more RF electrodes are mounted on separate wiresegments. The wire segments can comprise expandable curves, loops, mesh,basket, or other structures to place the RF electrodes in separatelocations.

When the wire segment structures are deployed, they flex to accommodatevarying vessel anatomy. Wire segment deployment can be coupled as in afixed basket configuration, or independent so that each wire segmentexpands as much as the anatomy requires. Deployment of the wire segmentsplaces the RF electrodes in good contact with the vessel wall.

The catheter device can be advanced and deployed in a renal artery toablate the renal nerves. Activating certain RF electrodes orcombinations by energizing from an external energy source throughinsulated conductors along the catheter, provides multiple discrete RFablation regions. Deployment can utilize self-expanding elastic forces,push/pull control structures, external retaining and recapture sheath,and other linkages and structures. An external sheath can be used toprotect and constrain the wire segments at the distal end of thecatheter during placement and withdrawal.

According to various embodiments, an intravascular catheter device hasmultiple wire segments near the distal end which move betweenlow-profile introduction configuration and larger-diameter deployedconfiguration. One or more RF electrodes are mounted on separate wiresegments. The wire segments can comprise expandable curves, loops, mesh,basket, or other structures to place the RF electrodes in separatelocations. When the wire segment structures are deployed, they flex toaccommodate varying vessel anatomy.

In one configuration, the wire segments are independent of other wires,so that each wire segment expands as much as the anatomy requires. Thewire segments can be insulated and serve as electrical conductorsbetween an external RF control unit and the electrodes. Activatingcertain RF electrodes or combinations by energizing from an externalenergy source through insulated conductors along the catheter, providesmultiple discrete RF ablation regions. Deployment can utilizeself-expanding elastic forces, push/pull control structures, externalretaining and recapture sheath, and other linkages and structures.

Deployment of the wire segments places the RF electrodes in good contactwith the vessel wall. An external sheath can be used to protect andconstrain the wire segments at the distal end of the catheter duringplacement and withdrawal. The catheter device can be advanced anddeployed in a renal artery to ablate the renal nerves. After positioningthe catheter's distal end within the renal artery, the sheath can beretracted to allow the wire segments to deploy and expand.

In other embodiments, the wire segments can be coupled as in a fixedbasket configuration, much like a mapping catheter. Some or allelectrodes can be energized simultaneously, or individual electrodes orsubsets of the electrodes can be energized to ablate one or more regionsof the perivascular nerves. Variations include number, circumferentiallocation, and axial location of wire segments and electrodes. Wiresegments can have spiral or other curvature. Wire segments can beconfigured as loops.

The proximal ends of the wires can be pushed or pulled to aid indeployment. The distal ends of the wire segments can be affixed to thecatheter. Lumen segments, or sliding attachment points, can be providedto control the wires but allow deployment movements.

Multiple wire segments with electrodes can be incorporated into acatheter, with push-pull deployment of the wire segments. Electrodes canbe shaped to displace tissue of the inner artery wall toward the outerartery wall so as to effectively shorten the distance separating theelectrode and the innervated target tissue adjacent the outer arterywall. The electrodes, according to various embodiments, include a tissuedisplacing tip having a radius that forcibly pushes the inner arterywall into the outer artery wall (thereby compressing intervening arterywall tissue) without penetrating the inner or outer artery walls. Insome embodiments, it may be desirable the permit the electrode tip topenetrate through the inner artery wall, but preferably not the outerartery wall. An external sheath can be used to cover the wires andelectrodes during advancement and retraction.

One or more temperature sensors, such as thermocouples, can be providedat the site of the electrodes to measure the temperature of theelectrodes. In some embodiments, a temperature sensor is positioned nearor at the site of each electrode, allowing for precision temperaturemeasurements at individual electrode locations of the ablation electrodearrangement.

Various embodiments of the disclosure are directed to apparatuses andmethods for renal denervation for treating hypertension. Hypertension isa chronic medical condition in which the blood pressure is elevated.Persistent hypertension is a significant risk factor associated with avariety of adverse medical conditions, including heart attacks, heartfailure, arterial aneurysms, and strokes. Persistent hypertension is aleading cause of chronic renal failure. Hyperactivity of the sympatheticnervous system serving the kidneys is associated with hypertension andits progression. Deactivation of nerves in the kidneys via renaldenervation can reduce blood pressure, and may be a viable treatmentoption for many patients with hypertension who do not respond toconventional drugs.

The kidneys are instrumental in a number of body processes, includingblood filtration, regulation of fluid balance, blood pressure control,electrolyte balance, and hormone production. One primary function of thekidneys is to remove toxins, mineral salts, and water from the blood toform urine. The kidneys receive about 20-25% of cardiac output throughthe renal arteries that branch left and right from the abdominal aorta,entering each kidney at the concave surface of the kidneys, the renalhilum.

Blood flows into the kidneys through the renal artery and the afferentarteriole, entering the filtration portion of the kidney, the renalcorpuscle. The renal corpuscle is composed of the glomerulus, a thicketof capillaries, surrounded by a fluid-filled, cup-like sac calledBowman's capsule. Solutes in the blood are filtered through the verythin capillary walls of the glomerulus due to the pressure gradient thatexists between the blood in the capillaries and the fluid in theBowman's capsule. The pressure gradient is controlled by the contractionor dilation of the arterioles. After filtration occurs, the filteredblood moves through the efferent arteriole and the peritubularcapillaries, converging in the interlobular veins, and finally exitingthe kidney through the renal vein.

Particles and fluid filtered from the blood move from the Bowman'scapsule through a number of tubules to a collecting duct. Urine isformed in the collecting duct and then exits through the ureter andbladder. The tubules are surrounded by the peritubular capillaries(containing the filtered blood). As the filtrate moves through thetubules and toward the collecting duct, nutrients, water, andelectrolytes, such as sodium and chloride, are reabsorbed into theblood.

The kidneys are innervated by the renal plexus which emanates primarilyfrom the aorticorenal ganglion. Renal ganglia are formed by the nervesof the renal plexus as the nerves follow along the course of the renalartery and into the kidney. The renal nerves are part of the autonomicnervous system which includes sympathetic and parasympatheticcomponents. The sympathetic nervous system is known to be the systemthat provides the bodies “fight or flight” response, whereas theparasympathetic nervous system provides the “rest and digest” response.Stimulation of sympathetic nerve activity triggers the sympatheticresponse which causes the kidneys to increase production of hormonesthat increase vasoconstriction and fluid retention. This process isreferred to as the renin-angiotensin -aldosterone-system (RAAS) responseto increased renal sympathetic nerve activity.

In response to a reduction in blood volume, the kidneys secrete renin,which stimulates the production of angiotensin. Angiotensin causes bloodvessels to constrict, resulting in increased blood pressure, and alsostimulates the secretion of the hormone aldosterone from the adrenalcortex. Aldosterone causes the tubules of the kidneys to increase thereabsorption of sodium and water, which increases the volume of fluid inthe body and blood pressure.

Congestive heart failure (CHF) is a condition that has been linked tokidney function. CHF occurs when the heart is unable to pump bloodeffectively throughout the body. When blood flow drops, renal functiondegrades because of insufficient perfusion of the blood within the renalcorpuscles. The decreased blood flow to the kidneys triggers an increasein sympathetic nervous system activity (i.e., the RAAS becomes tooactive) that causes the kidneys to secrete hormones that increase fluidretention and vasorestriction. Fluid retention and vasorestriction inturn increases the peripheral resistance of the circulatory system,placing an even greater load on the heart, which diminishes blood flowfurther. If the deterioration in cardiac and renal functioningcontinues, eventually the body becomes overwhelmed, and an episode ofheart failure decompensation occurs, often leading to hospitalization ofthe patient.

FIG. 1 is an illustration of a right kidney 10 and renal vasculatureincluding a renal artery 12 branching laterally from the abdominal aorta20. In FIG. 1, only the right kidney 10 is shown for purposes ofsimplicity of explanation, but reference will be made herein to bothright and left kidneys and associated renal vasculature and nervoussystem structures, all of which are contemplated within the context ofembodiments of the disclosure. The renal artery 12 is purposefully shownto be disproportionately larger than the right kidney 10 and abdominalaorta 20 in order to facilitate discussion of various features andembodiments of the present disclosure.

The right and left kidneys are supplied with blood from the right andleft renal arteries that branch from respective right and left lateralsurfaces of the abdominal aorta 20. Each of the right and left renalarteries is directed across the crus of the diaphragm, so as to formnearly a right angle with the abdominal aorta 20. The right and leftrenal arteries extend generally from the abdominal aorta 20 torespective renal sinuses proximate the hilum 17 of the kidneys, andbranch into segmental arteries and then interlobular arteries within thekidney 10. The interlobular arteries radiate outward, penetrating therenal capsule and extending through the renal columns between the renalpyramids. Typically, the kidneys receive about 20% of total cardiacoutput which, for normal persons, represents about 1200 mL of blood flowthrough the kidneys per minute.

The primary function of the kidneys is to maintain water and electrolytebalance for the body by controlling the production and concentration ofurine. In producing urine, the kidneys excrete wastes such as urea andammonium. The kidneys also control reabsorption of glucose and aminoacids, and are important in the production of hormones including vitaminD, renin and erythropoietin.

An important secondary function of the kidneys is to control metabolichomeostasis of the body. Controlling hemostatic functions includeregulating electrolytes, acid-base balance, and blood pressure. Forexample, the kidneys are responsible for regulating blood volume andpressure by adjusting volume of water lost in the urine and releasingerythropoietin and renin, for example. The kidneys also regulate plasmaion concentrations (e.g., sodium, potassium, chloride ions, and calciumion levels) by controlling the quantities lost in the urine and thesynthesis of calcitrol. Other hemostatic functions controlled by thekidneys include stabilizing blood pH by controlling loss of hydrogen andbicarbonate ions in the urine, conserving valuable nutrients bypreventing their excretion, and assisting the liver with detoxification.

Also shown in FIG. 1 is the right suprarenal gland 11, commonly referredto as the right adrenal gland. The suprarenal gland 11 is a star-shapedendocrine gland that rests on top of the kidney 10. The primary functionof the suprarenal glands (left and right) is to regulate the stressresponse of the body through the synthesis of corticosteroids andcatecholamines, including cortisol and adrenaline (epinephrine),respectively. Encompassing the kidneys 10, suprarenal glands 11, renalvessels 12, and adjacent perirenal fat is the renal fascia, e.g.,Gerota's fascia, (not shown), which is a fascial pouch derived fromextraperitoneal connective tissue.

The autonomic nervous system of the body controls involuntary actions ofthe smooth muscles in blood vessels, the digestive system, heart, andglands. The autonomic nervous system is divided into the sympatheticnervous system and the parasympathetic nervous system. In general terms,the parasympathetic nervous system prepares the body for rest bylowering heart rate, lowering blood pressure, and stimulating digestion.The sympathetic nervous system effectuates the body's fight-or-flightresponse by increasing heart rate, increasing blood pressure, andincreasing metabolism.

In the autonomic nervous system, fibers originating from the centralnervous system and extending to the various ganglia are referred to aspreganglionic fibers, while those extending from the ganglia to theeffector organ are referred to as postganglionic fibers. Activation ofthe sympathetic nervous system is effected through the release ofadrenaline (epinephrine) and to a lesser extent norepinephrine from thesuprarenal glands 11. This release of adrenaline is triggered by theneurotransmitter acetylcholine released from preganglionic sympatheticnerves.

The kidneys and ureters (not shown) are innervated by the renal nerves14. FIGS. 1 and 2A-2B illustrate sympathetic innervation of the renalvasculature, primarily innervation of the renal artery 12. The primaryfunctions of sympathetic innervation of the renal vasculature includeregulation of renal blood flow and pressure, stimulation of reninrelease, and direct stimulation of water and sodium ion reabsorption.

Most of the nerves innervating the renal vasculature are sympatheticpostganglionic fibers arising from the superior mesenteric ganglion 26.The renal nerves 14 extend generally axially along the renal arteries12, enter the kidneys 10 at the hilum 17, follow the branches of therenal arteries 12 within the kidney 10, and extend to individualnephrons. Other renal ganglia, such as the renal ganglia 24, superiormesenteric ganglion 26, the left and right aorticorenal ganglia 22, andceliac ganglia 28 also innervate the renal vasculature. The celiacganglion 28 is joined by the greater thoracic splanchnic nerve (greaterTSN). The aorticorenal ganglia 26 is joined by the lesser thoracicsplanchnic nerve (lesser TSN) and innervates the greater part of therenal plexus.

Sympathetic signals to the kidney 10 are communicated via innervatedrenal vasculature that originates primarily at spinal segments T10-T12and L1. Parasympathetic signals originate primarily at spinal segmentsS2-S4 and from the medulla oblongata of the lower brain. Sympatheticnerve traffic travels through the sympathetic trunk ganglia, where somemay synapse, while others synapse at the aorticorenal ganglion 22 (viathe lesser thoracic splanchnic nerve, i.e., lesser TSN) and the renalganglion 24 (via the least thoracic splanchnic nerve, i.e., least TSN).The postsynaptic sympathetic signals then travel along nerves 14 of therenal artery 12 to the kidney 10. Presynaptic parasympathetic signalstravel to sites near the kidney 10 before they synapse on or near thekidney 10.

With particular reference to FIG. 2A, the renal artery 12, as with mostarteries and arterioles, is lined with smooth muscle 34 that controlsthe diameter of the renal artery lumen 13. Smooth muscle, in general, isan involuntary non-striated muscle found within the media layer of largeand small arteries and veins, as well as various organs. The glomeruliof the kidneys, for example, contain a smooth muscle-like cell calledthe mesangial cell. Smooth muscle is fundamentally different fromskeletal muscle and cardiac muscle in terms of structure, function,excitation-contraction coupling, and mechanism of contraction.

Smooth muscle cells can be stimulated to contract or relax by theautonomic nervous system, but can also react on stimuli from neighboringcells and in response to hormones and blood borne electrolytes andagents (e.g., vasodilators or vasoconstrictors). Specialized smoothmuscle cells within the afferent arteriole of the juxtaglomerularapparatus of kidney 10, for example, produces renin which activates theangiotension II system.

The renal nerves 14 innervate the smooth muscle 34 of the renal arterywall 15 and extend lengthwise in a generally axial or longitudinalmanner along the renal artery wall 15. The smooth muscle 34 surroundsthe renal artery circumferentially, and extends lengthwise in adirection generally transverse to the longitudinal orientation of therenal nerves 14, as is depicted in FIG. 2B.

The smooth muscle 34 of the renal artery 12 is under involuntary controlof the autonomic nervous system. An increase in sympathetic activity,for example, tends to contract the smooth muscle 34, which reduces thediameter of the renal artery lumen 13 and decreases blood perfusion. Adecrease in sympathetic activity tends to cause the smooth muscle 34 torelax, resulting in vessel dilation and an increase in the renal arterylumen diameter and blood perfusion. Conversely, increasedparasympathetic activity tends to relax the smooth muscle 34, whiledecreased parasympathetic activity tends to cause smooth musclecontraction.

FIG. 3A shows a segment of a longitudinal cross-section through a renalartery, and illustrates various tissue layers of the wall 15 of therenal artery 12. The innermost layer of the renal artery 12 is theendothelium 30, which is the innermost layer of the intima 32 and issupported by an internal elastic membrane. The endothelium 30 is asingle layer of cells that contacts the blood flowing though the vessellumen 13. Endothelium cells are typically polygonal, oval, or fusiform,and have very distinct round or oval nuclei. Cells of the endothelium 30are involved in several vascular functions, including control of bloodpressure by way of vasoconstriction and vasodilation, blood clotting,and acting as a barrier layer between contents within the lumen 13 andsurrounding tissue, such as the membrane of the intima 32 separating theintima 32 from the media 34, and the adventitia 36. The membrane ormaceration of the intima 32 is a fine, transparent, colorless structurewhich is highly elastic, and commonly has a longitudinal corrugatedpattern.

Adjacent the intima 32 is the media 33, which is the middle layer of therenal artery 12. The media is made up of smooth muscle 34 and elastictissue. The media 33 can be readily identified by its color and by thetransverse arrangement of its fibers. More particularly, the media 33consists principally of bundles of smooth muscle fibers 34 arranged in athin plate-like manner or lamellae and disposed circularly around thearterial wall 15. The outermost layer of the renal artery wall 15 is theadventitia 36, which is made up of connective tissue. The adventitia 36includes fibroblast cells 38 that play an important role in woundhealing.

A perivascular region 37 is shown adjacent and peripheral to theadventitia 36 of the renal artery wall 15. A renal nerve 14 is shownproximate the adventitia 36 and passing through a portion of theperivascular region 37. The renal nerve 14 is shown extendingsubstantially longitudinally along the outer wall 15 of the renal artery12. The main trunk of the renal nerves 14 generally lies in or on theadventitia 36 of the renal artery 12, often passing through theperivascular region 37, with certain branches coursing into the media 33to enervate the renal artery smooth muscle 34.

Embodiments of the disclosure may be implemented to provide varyingdegrees of denervation therapy to innervated renal vasculature. Forexample, embodiments of the disclosure may provide for control of theextent and relative permanency of renal nerve impulse transmissioninterruption achieved by denervation therapy delivered using a treatmentapparatus of the disclosure. The extent and relative permanency of renalnerve injury may be tailored to achieve a desired reduction insympathetic nerve activity (including a partial or complete block) andto achieve a desired degree of permanency (including temporary orirreversible injury).

Returning to FIGS. 3B and 3C, the portion of the renal nerve 14 shown inFIGS. 3B and 3C includes bundles 14 a of nerve fibers 14 b eachcomprising axons or dendrites that originate or terminate on cell bodiesor neurons located in ganglia or on the spinal cord, or in the brain.Supporting tissue structures 14 c of the nerve 14 include theendoneurium (surrounding nerve axon fibers), perineurium (surroundsfiber groups to form a fascicle), and epineurium (binds fascicles intonerves), which serve to separate and support nerve fibers 14 b andbundles 14 a. In particular, the endoneurium, also referred to as theendoneurium tube or tubule, is a layer of delicate connective tissuethat encloses the myelin sheath of a nerve fiber 14 b within afasciculus.

Major components of a neuron include the soma, which is the central partof the neuron that includes the nucleus, cellular extensions calleddendrites, and axons, which are cable-like projections that carry nervesignals. The axon terminal contains synapses, which are specializedstructures where neurotransmitter chemicals are released in order tocommunicate with target tissues. The axons of many neurons of theperipheral nervous system are sheathed in myelin, which is formed by atype of glial cell known as Schwann cells. The myelinating Schwann cellsare wrapped around the axon, leaving the axolemma relatively uncoveredat regularly spaced nodes, called nodes of Ranvier. Myelination of axonsenables an especially rapid mode of electrical impulse propagationcalled saltation.

In some embodiments, a treatment apparatus of the disclosure may beimplemented to deliver denervation therapy that causes transient andreversible injury to renal nerve fibers 14 b. In other embodiments, atreatment apparatus of the disclosure may be implemented to deliverdenervation therapy that causes more severe injury to renal nerve fibers14 b, which may be reversible if the therapy is terminated in a timelymanner. In preferred embodiments, a treatment apparatus of thedisclosure may be implemented to deliver denervation therapy that causessevere and irreversible injury to renal nerve fibers 14 b, resulting inpermanent cessation of renal sympathetic nerve activity. For example, atreatment apparatus may be implemented to deliver a denervation therapythat disrupts nerve fiber morphology to a degree sufficient tophysically separate the endoneurium tube of the nerve fiber 14 b, whichcan prevent regeneration and re-innervation processes.

By way of example, and in accordance with Seddon's classification as isknown in the art, a treatment apparatus of the disclosure may beimplemented to deliver a denervation therapy that interrupts conductionof nerve impulses along the renal nerve fibers 14 b by imparting damageto the renal nerve fibers 14 b consistent with neruapraxia. Neurapraxiadescribes nerve damage in which there is no disruption of the nervefiber 14 b or its sheath. In this case, there is an interruption inconduction of the nerve impulse down the nerve fiber, with recoverytaking place within hours to months without true regeneration, asWallerian degeneration does not occur. Wallerian degeneration refers toa process in which the part of the axon separated from the neuron's cellnucleus degenerates. This process is also known as anterogradedegeneration. Neurapraxia is the mildest form of nerve injury that maybe imparted to renal nerve fibers 14 b by use of a treatment apparatusaccording to embodiments of the disclosure.

A treatment apparatus may be implemented to interrupt conduction ofnerve impulses along the renal nerve fibers 14 b by imparting damage tothe renal nerve fibers consistent with axonotmesis. Axonotmesis involvesloss of the relative continuity of the axon of a nerve fiber and itscovering of myelin, but preservation of the connective tissue frameworkof the nerve fiber. In this case, the encapsulating support tissue 14 cof the nerve fiber 14 b are preserved. Because axonal continuity islost, Wallerian degeneration occurs. Recovery from axonotmesis occursonly through regeneration of the axons, a process requiring time on theorder of several weeks or months. Electrically, the nerve fiber 14 bshows rapid and complete degeneration. Regeneration and re-innervationmay occur as long as the endoneural tubes are intact.

A treatment apparatus may be implemented to interrupt conduction ofnerve impulses along the renal nerve fibers 14 b by imparting damage tothe renal nerve fibers 14 b consistent with neurotmesis. Neurotmesis,according to Seddon's classification, is the most serious nerve injuryin the scheme. In this type of injury, both the nerve fiber 14 b and thenerve sheath are disrupted. While partial recovery may occur, completerecovery is not possible. Neurotmesis involves loss of continuity of theaxon and the encapsulating connective tissue 14 c, resulting in acomplete loss of autonomic function, in the case of renal nerve fibers14 b. If the nerve fiber 14 b has been completely divided, axonalregeneration causes a neuroma to form in the proximal stump.

A more stratified classification of neurotmesis nerve damage may befound by reference to the Sunderland System as is known in the art. TheSunderland System defines five degrees of nerve damage, the first two ofwhich correspond closely with neurapraxia and axonotmesis of Seddon'sclassification. The latter three Sunderland System classificationsdescribe different levels of neurotmesis nerve damage.

The first and second degrees of nerve injury in the Sunderland systemare analogous to Seddon's neurapraxia and axonotmesis, respectively.Third degree nerve injury, according to the Sunderland System, involvesdisruption of the endoneurium, with the epineurium and perineuriumremaining intact. Recovery may range from poor to complete depending onthe degree of intrafascicular fibrosis. A fourth degree nerve injuryinvolves interruption of all neural and supporting elements, with theepineurium remaining intact. The nerve is usually enlarged. Fifth degreenerve injury involves complete transection of the nerve fiber 14 b withloss of continuity.

Turning now to FIG. 4A, there is illustrated an apparatus for ablatingtarget tissue of a vessel of the body in accordance with variousembodiments. According to some embodiments, and as shown in FIG. 4A, theapparatus includes a sheath 119 having a lumen and a length sufficientto access a target vessel of a patient, such as the patient's renalartery, relative to a percutaneous access location. The apparatusfurther includes a catheter 100 which includes a flexible shaft 104having a proximal end, a distal end, and a length. The length of theshaft 104 is sufficient to access the target vessel, such as a patient'srenal artery 12, relative to a percutaneous access location. The shaft104 of the catheter 100 is dimensioned for displacement within the lumenof the sheath 119, and is extendible beyond a distal tip of the sheath119.

A multiplicity of elongated resilient members 131 are provided at thedistal end of the catheter's shaft 104. In the representative embodimentshown in FIG. 4A, four elongated resilient members 131 a-131 d areprovided at the distal end of the catheter's shaft 104. Each of theelongated resilient members 131 a-131 d is mounted along a longitudinallength of the distal end of the shaft 104, and engages the shaft 104 attwo or more longitudinally spaced-apart locations. The elongatedresilient members 131 a-131 d are mounted on the shaft 104 so that eachis extensible radially from the shaft 104 at regions defined between thelongitudinally spaced-apart engagement locations. The elongatedresilient members 131 a-131 d are formed of a material that produceselastic forces in the resilient members 131 a-131 d sufficient to causeself-expansion of the resilient members 131 a-131 d when the catheter100 and the resilient members 131 a-131 d are axially extended beyondthe distal tip of the shaft 104. For example, the resilient members 131a-131 d can be formed from a flexible electrically conductive materialthat facilitates flexing of the resilient members 131 a-131 d toaccommodate variations in renal artery anatomy.

One or more electrodes 120 are mounted on each of the resilient members131 a-131 d at the radially extensible regions. In the representativeembodiment shown in FIG. 4A, one electrode 120 a-120 d is shown mountedon each of the four resilient members 131 a-131 d at an apex locationbetween longitudinally spaced-apart engagement locations of the shaft104. A conductor arrangement electrically couples to the one or moreelectrodes 120 mounted on each of the resilient members 131 a-131 d andextends along the shaft 104 to a proximal end of the catheter 100.

In some embodiments, each of the resilient members 131 a-131 d defines aconductor that extends along the shaft 104 and provides for electricalconnectivity with the electrodes 120 a-120 d at a proximal end of thecatheter 100. The resilient members 131 a-131 can be covered with aninsulating sleeve or coating over the region that extends along thelength of the shaft 104. In other embodiments, separate lumens of theshaft 104 may be dimensioned to receive one of the resilient members 131a-131 d, which may include an inner wall of insulating material inresilient member configurations that do not include an insulating sleeveor coating. In further embodiments, each of the resilient members 131a-131 d can be coupled to a respective electrical conductor near thedistal end of the catheter 100, and the electrical conductors can extendalong the shaft and be accessible at the proximal end of the catheter100.

The elongated resilient members 131 a-131 d are preferably constructedfrom a resilient conductive alloy that has a shape memory. As is bestseen in FIG. 4C, the elongated resilient members 131 a-131 d arecollapsible when encompassed within the lumen of the sheath 119 orwithin the lumen of a target vessel, such as a patient's renal artery12. When axially extended beyond the distal tip of the sheath 119, theresilient members 131 a-131 d expand radially outwardly from the shaft104 at the regions defined between the longitudinally spaced-apartengagement locations. The electrodes 120 a-120 d mounted at or nearapical locations of the resilient members 131 a-131 d are movedoutwardly and into forced engagement with the inner wall of the targetvessel by the outwardly expanding resilient member 131 a-131 d. In thedeployed configuration, the multiple resilient members 131 a-131 dprovide for enhanced apposition of the electrodes 120 a-120 d within thetarget vessel, particularly for irregularities along the inner wall ofthe vessel.

According to various embodiments, the resilient members 131 a-131 d arearranged about a perimeter of the catheter's shaft 104 so that theelectrodes 120 a-120 d are positioned at disparate locations of a wallof the target vessel, such as the renal artery. For example, theresilient members 131 a-131 d are arranged about the perimeter of thecatheter's shaft 104 so that the electrodes 120 a-120 d form a generallyspiral shape to facilitate formation of a spiral lesion in a wall of therenal artery when the catheter 100 and the resilient members 131 a-131 dare axially extended beyond the distal tip of the sheath 119.

In some embodiments, the resilient members 131 a-131 d are mountedstructurally independently of one another along the longitudinal lengthof the distal end of the shaft 104. The shape memories of the resilientmembers 131 a-131 d are preferably selected so that the resilientmembers 131 a-131 d maintain a spaced-apart relationship when in theirexpanded deployed configuration. In such configurations, the resilientmembers 131 a-131 d need not be covered by an insulating sleeve orcoating, although such as sleeve or coating can be included if desired.According to other embodiments that utilize closely spaced resilientmembers 131 a-131 d, it may be desirable to cover the resilient members131 a-131 d proximal and distal to the electrode(s) 120 a-120 d with aninsulating sleeve or coating. FIG. 11 illustrates a resilient member 131having an insulating sleeve or coating 137 covering portions of theresilient member 131 proximal and distal to an electrode 120 supportedby the resilient member 131.

In accordance with various embodiments, a multiplicity of resilientmembers 131 are mounted in a structurally cooperative configurationrelative to one another along the longitudinal length of the distal endof the shaft 104. Illustrative examples of such embodiments are shown inFIGS. 12-15. FIG. 12, for example, shows a wire segment arrangement 127formed from a number of resilient members 131 and having a basket ormesh configuration. Each of the resilient members 131 of the basket ormesh has a generally arcuate shape with opposing ends that engage theshaft 104 at common distal and proximal circumferential mountingregions.

Each of the resilient members 131 in FIG. 12 is shown to support amultiplicity of electrodes 120 (e.g., 6 electrodes 120). In someembodiments, the electrodes 120 supported by individual resilientmembers 131 are connected in series. In other embodiments, all or atleast some of the electrodes 120 supported by individual resilientmembers 131 are connected by way of a separate conductor. In suchembodiments, all or at least some of the electrodes 120 supported byindividual resilient members 131 are individually controllable, allowingfor selective activation and deactivation of electrodes 120 of thebasket or mesh arrangements 127.

The resilient members 131 of a wire segment arrangement 127 can bearranged to form expandable curves or loops. Illustrative examples ofother wire segment arrangement configurations 127 are shown in FIGS.13-15. These and other wire segment arrangements 127 are contemplated,which may vary in terms of number, circumferential location, and axiallocation of wire segments and electrodes.

Some or all electrodes 120 of a wire segment arrangement 127 can beenergized concurrently, or individual electrodes 120 or subsets of theelectrodes 120 can be energized to ablate one or more regions of theperivascular nerves. For example, the electrodes 120 can be individuallyenergizable to produce multiple discrete ablation regions of the renalartery. Selective activation and deactivation of electrodes 120 of oneor more resilient members 131 of a wire segment arrangement 127advantageously provides for formation of lesions having a wide varietyof shapes (e.g., spiral, circumferential, spot) and sizes (e.g., such asby increasing or decreasing the number of activated electrodes 120 whencreating a lesion). These and other embodiments of the disclosurefacilitate formation of lesions in the target vessel having desiredshapes and sizes (e.g., a full revolution of a target vessel's wall)without having to reposition the catheter shaft 104 during the ablationprocedure.

FIG. 4B illustrates an apparatus for ablating target tissue of a vesselof the body in accordance with various embodiments. In the embodimentshown in FIG. 4B, a catheter 100 includes a multiplicity of elongatedresilient members 131 mounted at the distal end of the catheter's shaft104, and is similar to the catheter embodiment shown in FIG. 4A. Each ofthe elongated resilient members 131 a-131 d is mounted along alongitudinal length of the distal end of the shaft 104, engage the shaft104 at two or more longitudinally spaced-apart locations, and iscollapsible when encompassed within the lumen of the sheath 119. Whenaxially extended beyond the distal tip of the sheath 119, the resilientmembers 131 a-131 d expand radially outwardly from the shaft 104,causing the electrodes 120 a-120 d mounted at or near apical locationsof the resilient members 131 a-131 d to move outwardly and into forcedengagement with the inner wall of the target vessel.

The embodiment shown in FIG. 4B includes temperature sensors 123provided at the wire segment arrangement at the distal end of thecatheter 100. As is illustrated in FIG. 4B, each of the elongatedresilient members 131 a-131 d supports a temperature sensor 123 a-123 d,such as a thermocouple, provided at or near an electrode 120 a-120 d ofthe elongated resilient members 131 a-131 d. Each of the temperaturesensors 123 a-123 d is coupled to a respective sensor wire, whichextends along the length of the shaft 104 of the catheter 100 and areaccessible at the proximal end of the catheter 100.

The sensor wires can be pliable insulated wires that wrap around theresilient members 131 in a barber pole manner. In other configurations,the sensor wires can run parallel, and be bonded, to the resilientmembers 131 a-131 d. In further embodiments, the resilient members 131a-131 d can be covered with an electrically insulating sleeve orcoating, in which case the sensor wires need not have an electricallyinsulating sleeve or coating.

FIGS. 5 and 6 illustrate a catheter 100 which includes a multiplicity ofelectrodes supported by a wire segment arrangement in deployed andretracted configurations, respectively, according to variousembodiments. FIGS. 5 and 6 illustrate the distal end of a catheter shaft104 which supports a wire segment arrangement and a retraction mechanismin accordance with low-profile embodiments of the disclosure. In theembodiment shown in FIG. 5, the catheter 100 includes a wire segmentarrangement comprising four elongated resilient members 131 a-131 d thatare spaced apart from one another both longitudinally andcircumferentially. Each of the four elongated resilient members 131a-131 d supports an electrode 120 a-120 d. The resilient members 131a-131 d and electrodes 120 a-120 d are arranged so that at least onefull revolution of a target vessel can be ablated without having toreposition the catheter 100 during the ablation procedure.

The catheter shaft 104 includes lumens through which a pair of controlwires 133 a, 133 b extend. The control wires 133 a, 133 b can besituated in a common lumen of the shaft 104 or in separate lumens. Thedistal ends of the control wires 133 a, 133 b are coupled to proximalends of the resilient members 131 a-131 d, which pass into the controlwire lumen(s) through a small hole or slit through the shaft wall. Aseal arrangement may be positioned within the control wire lumen(s)proximal to the wire segment arrangements to prevent blood from passinginto the shaft 104 proximally of the seal arrangement.

In various embodiments, the control wires 133 a, 133 b are coupled tothe resilient members 131 a-131 d to provide push-pull deployment andretraction of the resilient members 131 a-131 d by a clinician. In someconfigurations, the distal ends of the two most distal resilient members131 a and 131 b are coupled to control wire 133 a, and the distal endsof the two most proximal resilient members 131 c and 131 d are coupledto control wire 133 b. Pushing on the control wire 133 a when theresilient members 131 a and 131 b are in a retracted configuration (seeFIG. 6) causes the resilient members 131 a and 131 b to move outwardlyfrom the shaft 104 into a deployed configuration (see FIG. 5). Pullingon the control wire 133 a when the resilient members 131 a and 131 b arein the deployed configuration causes the resilient members 131 a and 131b to move inwardly into the control wire lumen(s) of the shaft 104 (asshown in the retracted configuration of see FIG. 6). Resilient members131 c and 131 d can be moved into deployed and retracted configurationsby manipulating control wires 133 b in the same manner as describedabove with respect to control wire 133 a.

In other embodiments, each of the resilient members 131 a-131 d iscoupled to a single control wire 133. In this configuration, pushing thecontrol wire 133 in a distal direction causes the resilient members 131a-131 d to move into the deployed configuration. Pulling the controlwire 133 in a proximal direction causes the resilient members 131 a-131d to move into the retracted configuration. In further embodiments, eachof the resilient members 131 a-131 d can be coupled to a separatecontrol wire 131. In this configuration, individual resilient members131 a-131 d can be moved into the deployed and retracted configurationsby pushing and pulling respective control wires 131 coupled toindividual resilient members 131 a-131 d. A sheath (not shown) can beused to cover the wire segment arrangement 131 a-131 d and electrodes120 a-120 d during advancement and extraction of the catheter 100 to andfrom the target vessel.

FIGS. 7 and 8 illustrate a catheter 100 which includes a multiplicity ofelectrodes supported by a wire segment arrangement and having a tissuedisplacing feature in accordance with various embodiments. For purposesof clarity of explanation, only one wire segment arrangement is shownsupporting a single electrode. The electrode shown in FIG. 7 includes atissue displacing tip 125 that protrudes from the electrode body 120.The length of the tissue displacing tip 125 is selected to limit thedisplacement depth of the tissue displacing tip 125 into the targetvessel wall. For example, and as shown in FIG. 8, the tissue displacingtip 125 of the electrode 120 has a length and radius that allows thetissue displacing tip 125 to forcibly displace tissue of the wall of therenal artery wall 12 to a prescribed depth, but not to pierce through atleast the outer wall of the renal artery 12. The tissue displacingelectrode 120 and tip 125 for the application shown in FIG. 8 typicallyhas a length no longer than about 2.5 mm.

Configuring the electrode 120 shown in FIGS. 7 and 8 to include a tissuedisplacing tip 125 effectively decreases the distance between theelectrode 120 and the target tissue, such as perivascular renal nerves,by compressing artery tissue between the inner and outer artery walls.Reducing the distance between the electrode 120 and the target tissueadvantageously reduces the extent of thermal injury to neighboringnon-target tissue and can provide for a reduction in current densitiesrequired to ablate perivascular renal nerves.

FIGS. 9 and 10 illustrate arrangements that facilitate controllableexpansion and retraction of a wire segment arrangement in accordancewith various embodiments. In the embodiment shown in FIG. 9, anelongated resilient member 131 supporting an electrode 120 has a distalend 143 fixedly positioned at an outer wall of the shaft 104. The distalend 143 of the resilient member 131 is preferably bonded or otherwiseattached to an inner wall mounting location of the shaft 104 via anaccess aperture 141. In FIG. 9, the resilient member 131 is shown in anexpanded deployed configuration, in which the electrode 120 is supportedat a lateral height, h₁, relative to the outer wall of the shaft 104. Invarious embodiments, the lateral height, h₁, can range between about 1mm and about 4.5 mm relative to the outer wall of the shaft 104.

A proximal end of the resilient member 131 is shown to be displaceablein response to proximally and distally directed forces applied to aproximal end of the resilient member 131 or other elongated member thatcouples to the proximal end of the resilient member 131. The proximalend of the resilient member 131 can be displaced through a travellength, l₁, sufficient to limit expansion and collapsing of theresilient member 131 within the lateral height dimension h₁, relative tothe outer wall of the shaft 104. When in its retracted configuration,the resilient member 131 is compressed against the shaft's outer walland lies essentially flat along the outer wall of the shaft 104,reducing the lateral height, h₁, to a little more than the combinedthickness of the electrode 120 and the resilient member 131 (e.g., acombined thickness of about 0.2 mm).

When the resilient member 131 is compressed against the shaft's outerwall, such as when a delivery sheath is advanced over the resilientmember 131, the proximal end of the resilient member 131 is forcedproximally into its lumen within or along the shaft 104. Advancement ofthe proximal end of the resilient member 131 into its lumen allows theresilient member 131 to assume a low profile against the exterior wallof the shaft 104. When the delivery sheath is removed, theself-expanding resilient member 131 expands to assume its pre-formedshape, causing the proximal end of the resilient member 131 to movesomewhat distally at least partially out of its lumen.

In some configurations, a distally directed force is applied on theproximal end of the resilient member 131 to achieve full expansion ofthe resilient member 131. In other configurations, elastic forces of thematerial that forms the resilient member 131 causes self-expansion ofthe resilient member 131 to its deployed configuration by relaxingtension on the resilient member 131. In various configurations, somedegree of distally directed force can be applied on the proximal end ofthe resilient member 131 to enhance self-expansion of the resilientmember 131 to its deployed configuration.

According to some embodiments, a control wire 133 is attached to thedistal end of the resilient member 131 and actuatable by a clinician atthe proximal end of the catheter 100, such as in the manner describedpreviously with regard to FIGS. 5 and 6. In other embodiments, a controlwire 133 is not used, and the retraction and expansion mechanismdiscussed above operates automatically in response to application andremoval of compressive force to and from the resilient member 131 duringuse.

In the embodiment shown in FIG. 10, a slidable stop arrangement is shownwhich includes a pair of stops 151 a, 151 b that capture at least asegment of the resilient member 131. A stop member 153 is mounted to theresilient member 131. The range of axial displacement of the resilientmember 131 in the distal direction is limited by contact between thestop member 153 and the distal stop 151 a. The range of axialdisplacement of the resilient member 131 in the proximal direction islimited by contact between the stop member 153 and the proximal stop 151b. The range of axial displacement of the resilient member 131 istherefore limited by the travel distance, l₂, defined between a pair ofstops 151 a, 151 b. This travel distance , l₂, limits the extent towhich the lateral height, h₂, of the resilient member 131 can be changedbetween expanded and collapsed configurations, The travel distance, l₂,is preferably selected to allow for full expansion of the resilientmember 131 in the deployed configuration, and full compression of theresilient member 131 to achieve a low profile retracted configuration.

When the resilient member 131 (or a control wire coupled to theresilient member 131) is pulled in the proximal direction so that thestop member 153 contacts the proximal stop 151 b, the resilient member131 supporting the electrode collapses toward the outer surface of theshaft 104 until a fully low profile retracted or collapsed configurationis achieved. When tension on the resilient member 131 is released and/ora distally directed force is applied, the stop member 153 advancestoward the distal stop 151 a, allowing the resilient member 131 toself-expand to its pre-formed deployed shape as the stop member 153advances toward the distal stop 151 a. When the stop member 153 contactsthe distal stop 151 a, the resilient member 131 achieves its deployedconfiguration. It is noted that the arrangements shown in FIGS. 9 and 10can be implemented within a lumen of the shaft 104, within a wall of theshaft 104, or in a side lumen extending at least in part along the outerwall of the shaft 104.

FIG. 16 shows a representative RF renal therapy apparatus 300 inaccordance with various embodiments of the disclosure. The apparatus 300illustrated in FIG. 16 includes external electrode activation circuitry320 which comprises power control circuitry 322 and timing controlcircuitry 324. The external electrode activation circuitry 320, whichincludes an RF generator, is coupled to temperature measuring circuitry328 and may be coupled to an optional impedance sensor 326. The catheter100 includes a shaft 104 that incorporates a lumen arrangement 105configured for receiving a variety of components, such as conductors,pharmacological agents, actuator elements, obturators, sensors, or othercomponents as needed or desired.

The RF generator of the external electrode activation circuitry 320 mayinclude a return pad electrode 330 that is configured to comfortablyengage the patient's back or other portion of the body near the kidneys.Radiofrequency energy produced by the RF generator is coupled to thetreatment element 101 at the distal end of the catheter 101 by theconductor arrangement 110 disposed in the lumen of the catheter's shaft104.

Renal denervation therapy using the apparatus shown in FIG. 16 istypically performed using the electrodes 120 supported by the wiresegment arrangement of the treatment element 101 positioned within therenal artery 12 and the return pad electrode 330 positioned on thepatient's back, with the RF generator operating in a monopolar mode. Inthis implementation, the electrodes 120 a-120 d, for example, areconfigured for operation in a unipolar configuration. In otherimplementations, the electrodes 120 supported by the wire segmentarrangement of the treatment element 101 can be configured for operationin a bipolar configuration, in which case the return electrode pad 330is not needed.

The radiofrequency energy flows through the electrodes 120 in accordancewith a predetermined activation sequence (e.g., sequential orconcurrent) causing ionic agitation, and therefore friction in theadjacent tissue of the renal artery.

In general, when renal artery tissue temperatures rise above about 113°F. (50° C.), protein is permanently damaged (including those of renalnerve fibers). For example, any mammalian tissue that is heated aboveabout 50° C. for even 1 second is killed. If heated over about 65° C.,collagen denatures and tissue shrinks If heated over about 65° C. and upto 100° C., cell walls break and oil separates from water. Above about100° C., tissue desiccates.

According to some embodiments, the electrode activation circuitry 320 isconfigured to control activation and deactivation of the electrodes 120in accordance with a predetermined energy delivery protocol and inresponse to signals received from temperature measuring circuitry 328.The electrode activation circuitry 320 controls radiofrequency energydelivered to the electrodes 120 so as to maintain the current densitiesat a level sufficient to cause heating of the target tissue to at leasta temperature of about 55° C.

In some embodiments, temperature sensors are situated at the treatmentelement 101 and provide for continuous monitoring of renal artery tissuetemperatures, and RF generator power is automatically adjusted so thatthe target temperatures are achieved and maintained. An impedance sensorarrangement 326 may be used to measure and monitor electrical impedanceduring RF denervation therapy, and the power and timing of the RFgenerator 320 may be moderated based on the impedance measurements or acombination of impedance and temperature measurements. The size of theablated area is determined largely by the size, number, and shape of theelectrodes 120 supported by the wire segment arrangement of thetreatment element 101, the power applied, and the duration of time theenergy is applied.

Marker bands 314 can be placed on one or multiple parts of the treatmentelement 101 to enable visualization during the procedure. Other portionsof the catheter 101, such as one or more portions of the shaft 104(e.g., at the hinge mechanism 356), may include a marker band 314. Themarker bands 314 may be solid or split bands of platinum or otherradiopaque metal, for example. Radiopaque materials are understood to bematerials capable of producing a relatively bright image on afluoroscopy screen or another imaging technique during a medicalprocedure. This relatively bright image aids the user in determiningspecific portions of the catheter 100, such as the tip of the catheter101, the treatment element 101, and the hinge 356, for example. A braidand/or electrodes of the catheter 100, according to some embodiments,can be radiopaque.

Various embodiments disclosed herein are generally described in thecontext of ablation of perivascular renal nerves for control ofhypertension. It is understood, however, that embodiments of thedisclosure have applicability in other contexts, such as performingablation from within other vessels of the body, including otherarteries, veins, and vasculature (e.g., cardiac and urinary vasculatureand vessels), and other tissues of the body, including various organs.

It is to be understood that even though numerous characteristics ofvarious embodiments have been set forth in the foregoing description,together with details of the structure and function of variousembodiments, this detailed description is illustrative only, and changesmay be made in detail, especially in matters of structure andarrangements of parts illustrated by the various embodiments to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. An apparatus, comprising: a sheath having a lumenand a length sufficient to access a patient's renal artery relative to apercutaneous access location; a catheter comprising a flexible shafthaving a proximal end, a distal end, and a length, the length of theshaft sufficient to access a patient's renal artery relative to thepercutaneous access location, the shaft dimensioned for displacementwithin the lumen of the sheath and extendible beyond a distal tip of thesheath; a plurality of elongated resilient members each mountedstructurally independent of one another along a longitudinal length ofthe distal end of the shaft, the resilient members engaging the shaft ata plurality of longitudinally spaced-apart locations and extensibleradially from the shaft at regions defined between the longitudinallyspaced-apart engagement locations; one or more electrodes mounted oneach of the resilient members at the radially extensible regions; and aplurality of conductors electrically coupled to the one or moreelectrodes and extending along the shaft of the catheter; the elongatedresilient members collapsible when encompassed within the lumen of thesheath and extensible radially outward from the shaft at the regionsdefined between the longitudinally spaced-apart engagement locationswhen the catheter and the resilient members are axially extended beyondthe distal tip of the sheath, wherein a proximal end of the elongatedresilient members is movable relative to the shaft, and wherein theelectrodes are distributed about a perimeter of the catheter shaft tofacilitate formation of a spiral lesion in a wall of the renal arterywhen the catheter and the resilient members are axially extended beyondthe distal tip of the sheath.
 2. The apparatus of claim 1, wherein theresilient members are arranged to form expandable curves or loops. 3.The apparatus of claim 1, wherein the resilient members are formed of aflexible electrically conductive material that facilitates flexing ofthe resilient members to accommodate variations in renal artery anatomy.4. The apparatus of claim 1, wherein each of the electrodes comprises atissue displacing tip.
 5. The apparatus of claim 4, wherein the tissuedisplacing tips are configured to forcibly displace tissue of an innerwall of the renal artery relative to an outer wall of the renal arteryto a prescribed depth, but not to pierce through at least the outer wallof the renal artery.
 6. The apparatus of claim 1, wherein the electrodesare individually energizable to produce multiple discrete ablationregions of the renal artery.
 7. The apparatus of claim 1, wherein theresilient members are formed of a material that produces elastic forcesin the resilient members sufficient to cause self-expansion of theresilient members when the catheter and the resilient members areaxially extended beyond the distal tip of the sheath.
 8. The apparatusof claim 1, wherein the resilient members are formed of a flexiblematerial that facilitates expansion and contraction of the resilientmembers in response to expansion and contraction control forces appliedto the resilient members.
 9. The apparatus of claim 1, wherein a portionof the resilient members between the electrodes is covered by anelectrical insulator.